1. Field of Invention
The present invention relates to a method pertaining to a transmitter and receiver unit in a mobile telephone system. The invention also relates to an arrangement for carrying out the method.
More specifically, the invention relates to a method and to an arrangement for mobile telephone systems in large buildings, and particularly in very tall buildings such as so-called skyscrapers. The mobile telephone system may be any known wireless mobile system, for instance a GSM system. The invention is described below with reference to a GSM system, although it will be understood that the invention is not restricted to this particular type of system. For instance, the system may be a PABX system or a wireless-LAN-system. The present invention can also be applied in fully internal wireless mobile telephone systems in large buildings, where the internal system is connected to the outside world via an existing telephone network.
2. Description of Related Art
The use of a mobile system in large buildings, and then particularly in skyscrapers, presents serious problems unless measures are taken in the buildings concerned. This is due to several reasons. One reason is the actual building itself, since a skyscraper will normally include a significant number of reinforcement bars, steel beams, etc., which tend to screen the building magnetically from the outside world. The metal coated panes of facade glass with which such buildings are normally covered to a large extent also have this affect. It is also necessary in a high building to install a large number of base stations which communicate with the mobile telephones and which are able to cover the whole of the building area. This can present a system problem with respect to the base station with which a given mobile telephone shall communicate.
Another problem is one of providing effective radio coverage within large buildings. When ground-mounted base stations are used, this is due to attenuation of the radio signals caused by the building, and consequently coverage will become poorer further into a building. By ground-mounted base stations is meant base stations that are placed outdoors.
A further problem resides in the requirement of a high network capacity in large buildings, owing to the large number of users in such buildings. For instance, if a high building has good radio contact with ground base stations the users in said building will take a large part of the capacity of such base stations, therewith reducing the base station capacity for users outside the building. Furthermore, there will often be interference between different base stations covering the building, resulting in poor speech quality and, at times, in lost connections.
Consequently, mutually separate internal mobile telephone systems are often installed in large and high buildings.
Skyscrapers and large buildings have been mentioned in the aforegoing. By large buildings is also meant large public complexes or buildings, such as airport buildings, railroad stations, restaurants, office buildings, and so on.
The present invention is not restricted to any particular type of building, but can be applied in all manner of buildings which due to their size and/or configuration necessitate the installation of separate systems that include comprehensive cabling, a large number of antennas, etc., when practicing known techniques, in order to obtain satisfactory mobile telephone traffic with good coverage within the building concerned. What is strived for is higher speech quality, better coverage and greater capacity.
Such separate installations include a local transceiver unit which is connected to the fixed part of a mobile telephone network installed in the building. The transceiver unit is a base transceiver station that corresponds to a typical base station in a GSM network. Cables are drawn from the transceiver unit to different stories or floors in the building, where one or more antennas are placed on each storey.
According to one embodiment, coaxial cables are drawn from the transceiver unit to passive antennas in the building, via so-called splitters. This solution is primarily intended for smaller buildings. It is not as effective in larger buildings, due to the high losses experienced in the coaxial cables, among other things.
Consequently, fibre optic cables are used in larger buildings between the transceiver unit and an active antenna unit at each storey, for instance. The active antenna unit converts light in the fibre optic cable to an RF-signal and vice versa, in addition to including a transceiver antenna. An installation of this nature may also be supplemented with a facility in which the active antenna unit also supplies passive antennas via splitters.
It is obvious that the known solutions to the problem of implementing mobile telephone systems in large buildings requires a large amount of coaxial cables and fibre optic cables to be laid in the building, and that a large number of splitters, combiners, antenna units and antennas must be installed. Such installation is very laborious and cost-demanding.
The present invention solves the aforesaid problems in a very simple and relatively very inexpensive manner.
The present invention thus relates to a method pertaining to a transceiver unit in a mobile telephone system in which the transceiver unit is installed in a building that includes a ventilation system for use for mobile telephone traffic within the building, said method being characterised by installing one or more antennas in one or more of the air ducts belonging to the building ventilation system and connecting said antennas to said transceiver unit.
The invention also relates to an arrangement that has essentially the characteristic features set forth in claim 7.